The search for new therapeutic agents has been greatly aided in recent years by a better understanding of the structure of enzymes and other biomolecules associated with target diseases. One important class of enzymes that has been the subject of extensive study is protein kinases.
Protein kinases mediate intracellular signal transduction. They do this by effecting a phosphoryl transfer from a nucleoside triphosphate to a protein acceptor that is involved in a signaling pathway. There are a number of kinases and pathways through which extracellular and other stimuli cause a variety of cellular responses to occur inside the cell. Examples of such stimuli include environmental and chemical stress signals (e.g., osmotic shock, heat shock, ultraviolet radiation, bacterial endotoxin, and H2O2), cytokines (e.g., interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF-α)), and growth factors (e.g., granulocyte macrophage-colony-stimulating factor (GM-CSF), and fibroblast growth factor (FGF)). An extracellular stimulus may affect one or more cellular responses related to cell growth, migration, differentiation, secretion of hormones, activation of transcription factors, muscle contraction, glucose metabolism, control of protein synthesis and regulation of cell cycle.
Many diseases are associated with abnormal cellular responses triggered by protein kinase-mediated events. These diseases include autoimmune diseases, inflammatory diseases, bone diseases, metabolic diseases, neurological and neurodegenerative diseases, cancer, cardiovascular diseases, allergies and asthma, Alzheimer's disease and hormone-related diseases. Accordingly, there has been a substantial effort in medicinal chemistry to find protein kinase inhibitors that are effective as therapeutic agents.
The Aurora family of serine/threonine kinases is essential for cell proliferation [Bischoff, J. R. & Plowman, G. D. (The Aurora/Ipl1p kinase family: regulators of chromosome segregation and cytokinesis) Trends in Cell Biology 9, 454-459 (1999); Giet, R. and Prigent, C. (Aurora/Ipl1p-related kinases, a new oncogenic family of mitotic serine-threonine kinases) Journal of Cell Science 112, 3591-3601 (1999); Nigg, E. A. (Mitotic kinases as regulators of cell division and its checkpoints) Nat. Rev. Mol. Cell. Biol. 2, 21-32 (2001); Adams, R. R, Carmena, M., and Earnshaw, W. C. (Chromosomal passengers and the (aurora) ABCs of mitosis) Trends in Cell Biology 11, 49-54 (2001)]. Inhibitors of the Aurora kinase family therefore have the potential to block growth of all tumour types.
The three known mammalian family members, Aurora-A (“1”), B (“2”) and C (“3”), are highly homologous proteins responsible for chromosome segregation, mitotic spindle function and cytokinesis. Aurora expression is low or undetectable in resting cells, with expression and activity peaking during the G2 and mitotic phases in cycling cells. In mammalian cells proposed substrates for Aurora include histone H3, a protein involved in chromosome condensation, and CENP-A, myosin II regulatory light chain, protein phosphatase 1, TPX2, all of which are required forcell division.
Since its discovery in 1997 the mammalian Aurora kinase family has been closely linked to tumorigenesis. The most compelling evidence for this is that over-expression of Aurora-A transforms rodent fibroblasts (Bischoff, J. R., et al. A homologue of Drosophila aurora kinase is oncogenic and amplified in human colorectal cancers. EMBO J. 17, 3052-3065 (1998)). Cells with elevated levels of this kinase contain multiple centrosomes and multipolar spindles, and rapidly become aneuploid. The oncogenic activity of Aurora kinases is likely to be linked to the generation of such genetic instability. Indeed, a correlation between amplification of the aurora-A locus and chromosomal instability in mammary and gastric tumours has been observed. (Miyoshi, Y., Iwao, K., Egawa, C., and Noguchi, S. Association of centrosomal kinase STK15/BTAK mRNA expression with chromosomal instability in human breast cancers. Int. J. Cancer 92, 370-373 (2001). (Sakakura, C. et al. Tumor-amplified kinase BTAK is amplified and overexpressed in gastric cancers with possible involvement in aneuploid formation. British Journal of Cancer 84, 824-831 (2001)). The Aurora kinases have been reported to be over-expressed in a wide range of human tumours. Elevated expression of Aurora-A has been detected in over 50% of colorectal (Bischoff, J. R., et al. A homologue of Drosophila aurora kinase is oncogenic and amplified in human colorectal cancers. EMBO J. 17, 3052-3065 (1998)) (Takahashi, T., et al. Centrosomal kinases, HsAIRk1 and HsAIRK3, are overexpressed in primary colorectal cancers. Jpn. J. Cancer Res. 91, 1007-1014 (2000)). ovarian (Gritsko, T. M. et al. Activation and overexpression of centrosome kinase BTAK/Aurora-A in human ovarian cancer. Clinical Cancer Research 9, 1420-1426 (2003)), and gastric tumors (Sakakura, C. et al. Tumor-amplified kinase BTAK is amplified and overexpressed in gastric cancers with possible involvement in aneuploid formation. British Journal of Cancer 84, 824-831 (2001)), and in 94% of invasive duct adenocarcinomas of the breast (Tanaka, T., et al. Centrosomal kinase AIK1 is overexpressed in invasive ductal carcinoma of the breast. Cancer Research. 59, 2041-2044 (1999)). High levels of Aurora-A have also been reported in renal, cervical, neuroblastoma, melanoma, lymphoma, pancreatic and prostate tumour cell lines. (Bischoff, J. R., et al. A homologue of Drosophila aurora kinase is oncogenic and amplified in human colorectal cancers. EMBO J. 17, 3052-3065 (1998) (Kimura, M., Matsuda, Y., Yoshioka, T., and Okano, Y. Cell cycle-dependent expression and centrosomal localization of a third human Aurora/Ipl1-related protein kinase, AIK3. Journal of Biological Chemistry 274, 7334-7340 (1999))(Zhou et al. Tumour amplifiec kinase STK15/BTAK induces centrosome amplification, aneuploidy and transformation Nature Genetics 20: 189-193 (1998))(Li et al. Overexpression of oncogenic STK15/BTAK/Aurora-A kinase in human pancreatic cancer Clin Cancer Res. 9(3):991-7 (2003)). Amplification/overexpression of Aurora-A is observed in human bladder cancers and amplification of Aurora-A is associated with aneuploidy and aggressive clinical behaviour (Sen S. et al Amplification/overexpression of a mitotic kinase gene in human bladder cancer J Natl Cancer Inst. 94(17):1320-9 (2002)). Moreover, amplification of the aurora-A locus (20q13) correlates with poor prognosis for patients with node-negative breast cancer (Isola, J. J., et al. Genetic aberrations detected by comparative genomic hybridization predict outcome in node-negative breast cancer. American Journal of Pathology 147, 905-911 (1995)). Aurora-B is highly expressed in multiple human tumour cell lines, including leukemic cells (Katayama et al. Human AIM-1: cDNA cloning and reduced expression during endomitosis in megakaryocyte-lineage cells. Gene 244:1-7)). Levels of this enzyme increase as a function of Duke's stage in primary colorectal cancers (Katayama, H. et al. Mitotic kinase expression and colorectal cancer progression. Journal of the National Cancer Institute 91, 1160-1162 (1999)). Aurora-C, which is normally only found in germ cells, is also over-expressed in a high percentage of primary colorectal cancers and in a variety of tumour cell lines including cervical adenocarinoma and breast carcinoma cells (Kimura, M., Matsuda, Y., Yoshioka, T., and Okano, Y. Cell cycle-dependent expression and centrosomal localization of a third human Aurora/Ipl1-related protein kinase, AIK3. Journal of Biological Chemistry 274, 7334-7340 (1999). (Takahashi, T., et al. Centrosomal kinases, HsAIRk1 and HsAIRK3, are overexpressed in primary colorectal cancers. Jpn. J. Cancer Res. 91, 1007-1014 (2000)).
Based on the known function of the Aurora kinases, inhibition of their activity should disrupt mitosis leading to cell cycle arrest. In vivo, an Aurora inhibitor therefore slows tumor growth and induces regression.
Elevated levels of all Aurora family members are observed in a wide variety of tumour cell lines. Aurora kinases are over-expressed in many human tumors and this is reported to be associated with chromosomal instability in mammary tumors (Miyoshi et al 2001 92, 370-373).
Aurora-2 is highly expressed in multiple human tumor cell lines and levels increase as a function of Duke's stage in primary colorectal cancers [Katayama, H. et al. (Mitotic kinase expression and colorectal cancer progression) Journal of the National Cancer Institute 91, 1160-1162 (1999)]. Aurora-2 plays a role in controlling the accurate segregation of chromosomes during mitosis. Misregulation of the cell cycle can lead to cellular proliferation and other abnormalities. In human colon cancer tissue, the Aurora-2 protein has been found to be over expressed [Bischoff et al., EMBO J., 17, 3052-3065 (1998); Schumacher et al., J. Cell Biol., 143, 1635-1646 (1998); Kimura et al., J. Biol. Chem., 272, 13766-13771 (1997)]. Aurora-2 is over-expressed in the majority of transformed cells. Bischoff et at found high levels of Aurora-2 in 96% of cell lines derived from lung, colon, renal, melanoma and breast tumors (Bischoff et al EMBO J. 1998 17, 3052-3065). Two extensive studies show elevated Aurora-2 in 54% and 68% (Bishoff et al EMBO J. 1998 17, 3052-3065)(Takahashi et al 2000 Jpn J Cancer Res. 91, 1007-1014) of colorectal tumours and in 94% of invasive duct adenocarcinomas of the breast (Tanaka et al 1999 59, 2041-2044).
Aurora-1 expression is elevated in cell lines derived from tumors of the colon, breast, lung, melanoma, kidney, ovary, pancreas, CNS, gastric tract and leukemias (Tatsuka et al 1998 58, 4811-4816).
High levels of Aurora-3 have been detected in several tumour cell lines, although it is restricted to testis in normal tissues (Kimura et al 1999 274, 7334-7340). Over-expression of Aurora-3 in a high percentage (c. 50%) of colorectal cancers has also been documented (Takahashi et al 2000 Jpn J Cancer Res. 91, 1007-1014). In contrast, the Aurora family is expressed at a low level in the majority of normal tissues, the exceptions being tissues with a high proportion of dividing cells such as the thymus and testis (Bischoff et al EMBO J. 1998 17, 3052-3065).
For further review of the role Aurora kinases play in proliferative disorders, see Bischoff, J. R. & Plowman, G. D. (The Aurora/Ipl1p kinase family: regulators of chromosome segregation and cytokinesis) Trends in Cell Biology 9, 454-459 (1999); Giet, R. and Prigent, C. (Aurora/Ipl1p-related kinases, a new oncogenic family of mitotic serine-threonine kinases) Journal of Cell Science 112, 3591-3601 (1999); Nigg, E. A. (Mitotic kinases as regulators of cell division and its checkpoints) Nat. Rev. Mol. Cell. Biol. 2, 21-32 (2001); Adams, R. R, Carmena, M., and Earnshaw, W. C. (Chromosomal passengers and the (aurora) ABCs of mitosis) Trends in Cell Biology 11, 49-54 (2001); and Dutertre, S., Descamps, S., & Prigent, P. (On the role of aurora-A in centrosome function) Oncogene 21, 6175-6183 (2002).
The type III receptor tyrosine kinase, Flt3, plays an important role in the maintenance, growth and development of hematopoietic and non-hematopoietic cells. [Scheijen, B, Griffin J D, Oncogene, 2002, 21, 3314-3333 and Reilly, J T, British Journal of Haematology, 2002, 116, 744-757]. FLT-3 regulates maintenance of stem cell/early progenitor pools as well the development of mature lymphoid and myeloid cells [Lyman, S, Jacobsen, S, Blood, 1998, 91, 1101-1134]. FLT-3 contains an intrinsic kinase domain that is activated upon ligand-mediated dimerization of the receptors. Upon activation, the kinase domain induces autophosphorylation of the receptor as well as the phosphorylation of various cytoplasmic proteins that help propogate the activation signal leading to growth, differentiation and survival. Some of the downstream regulators of FLT-3 receptor signaling include, PLCγ, PI3-kinase, Grb-2, SHIP and Src related kinases [Scheijen, B, Griffin J D, Oncogene, 2002, 21, 3314-3333]. FLT-3 kinase plays a role in a variety of hematopoietic and non-hematopoietic malignancies. Mutations that induce ligand independent activation of FLT-3 have been implicated in acute-myelogenous leukemia (AML), acute lymphocytic leukemia (ALL), mastocytosis and gastrointestinal stromal tumor (GIST). These mutations include single amino acid changes in the kinase domain or internal tandem duplications, point mutations or in-frame deletions of the juxtamembrane region of the receptors. In addition to activating mutations, ligand dependent (autocrine or paracrine) stimulation of over-expressed wild-type FLT-3 contributes to the malignant phenotype [Scheijen, B, Griffin J D, Oncogene, 2002, 21, 3314-3333]. See also Sawyer, C. l. (Finding the next Gleevec: FLT3 targeted kinase inhibitor therapy for acute myeloid leukaemia) Cancer Cell. 1, 413-415 (2002).
Tri- or tetra-substituted pyrimidine derivatives useful as kinase inhibitors are known in the art. Typically, these pyrimidine derivatives are 2,4,6- or 2,4,5,6-substituted, as shown below:

Known methods for preparing such pyrimidine derivatives have many synthetic drawbacks such as lacking the ability to regioselectively introduce substituents at the 2-, 4-, or 6-position in high yields. See M. Botta, Nucleosides Nucleotides, 13, 8, 1994, 1769-78; M. Ban, Bioorg. Med. Chem., 6, 7, 1998, 1057-68; Y. Fellahi, Eur. J. Med. Chem. Chim. Ther., 31, 1, 1996, 77-82; T. J. Delia, J. Het. Chem., 35, 2, 1998, 269-74; H. Uchel, Tetraheron Lett., 36, 52, 1995, 9457-60; and Y. Nezu, Pestic. Sci., 47, 2, 1996, 115-24.
There is a need for a synthetic process that can be readily used to prepare the tri- or tetra-substituted pyrimidine derivatives on a large scale. There is also a need for a process that employs minimal steps and utilizes readily available starting materials and simple reaction media. Ideally, such a process will be easy to scale up, if need be, and will be inexpensive. There is also a need for a process that does not lead to regioisomeric intermediate mixtures that must be separated by, e.g., chromatographic methods. Such separations reduce the overall yields.
It would be desirable to have a synthetic process to produce tri- or tetra-substituted pyrimidine derivatives that possesses the above advantages and thereby improves upon the currently available processes.